The present invention relates to a supported catalyst for producing a styrenic polymer having a syndiotactic configuration. More particularly, the present invention relates to a supported catalyst which is used to prepare a syndiotactic styrenic polymer with high productivity and with significantly diminished reactor fouling when a stirring-tank reactor is employed.
Syndiotactic polystyrene (sPS) was first synthesized in 1985, using the homogeneous organometallic catalytic system based on a titanium compound and methylaluminoxane (MAO). Syndiotactic polystyrene is a very attractive polymer. The polymer shows a low specific gravity, a low dielectric constant, a high modulus of elasticity and an excellent resistance to chemicals. Accordingly the syndiotactic polystyrene has become a promising material for various applications in the automotive, electronic and packaging industries.
A large number of patents on this subject have been filed in recent years. The early patents were dedicated to the synthesis, particularly to the nature of the catalyst and the later patents to the cocatalyst and the other minor components. Then the problems of the polymerization process were more and more addressed.
In the commercialization of syndiotactic polystyrene, problems, such as serious reactor fouling, and low flow-ability of the product powder resulted from unsatisfactory morphology, remain unsolved if a homogeneous catalyst is used when a stirring-tank reactor is employed. To solve these problems, two alternative routes seem to be possible: (a) specially designed reactor, and (b) catalyst supported on insoluble solid. The reactor design is not in the scope of this patent and what to be concerned here is the supported catalyst system.
The activity of a supported metallocene catalyst is, generally, much lower than that of the corresponding homogeneous catalyst by the order of magnitude of 2-3. The polymerization activity of syndiotactic styrene is, generally, much lower than that of polyolefin. Therefore it is very difficult to prepare a supported catalyst having acceptable activity for producing a syndiotactic polystyrene. In order to have the high activity and polymerization efficiency similar to the homogeneous catalyst, the supported catalyst should maintain the basic metallocene structure, and in order to prevent fouling, the catalyst should not be separated from the support At) during polymerization.
So far, four basic methods have been developed for metallocene catalyst systems for production of polyolefin as follow:
1. direct adsorption of metallocene into the support surface involving physisorption or chemisorption of metallocene (direct heterogenization);
2. initial adsorption of methylaluminoxane (MAO) into the support, followed by adsorption of metallocene (indirect heterogenization);
3. covalent bonding of metallocene to a carrier by a ligand, followed by activation with MAO; and
4. use of an organic compound which is able to react with the hydroxyl group of an inorganic support surface such as silica and to form a complex with metallocene to be supported, which is represented by the following reaction as one example:
Sixe2x80x94OH+HOxe2x80x94Rxe2x80x94OHxe2x86x92Sixe2x80x94Rxe2x80x94OHxe2x86x92Sixe2x80x94Oxe2x80x94Rxe2x80x94O . . . Metallocene
where R is a hydrocarbon compound.
Either direct loading of a metallocene catalyst on a support (Method 1) or indirect loading on a MAO treated support (Method 2) does not provide a good activity for styrenic polymerization. Method 3 relates to a complex chemistry and difficulties arise when bonding the metallocene to the support surface (Soga, Stud Surf .Sci. Cat. 1994, 89, 307). A spacer between support and metallocene was introduced in Method 4, but the results, as reported by Spitz et al. (Macromol. Chem. Phys. 1999, 200, 1453), show that there is no any enhancement of styrene polymerization activity.
Until now, very few reports can be seen in the area of supported catalyst for producing syndiotactic polystyrene. Silica (Kaminsky et al., J. Polym. Sci.: Part A: Polym. Chem. 1999, 37, 2959), alumina (Spitz et al., Macromol. Chem. Phys. 1999, 200, 1453) and polymer (Yu et al., J. Polym. Sci.: Part A: Polym. Chem. 1996, 34, 2237) have been used as a support for preparation of a supported catalyst for producing syndiotactic polystyrene. Unfortunately, all these supported catalysts are not applicable because of extremely low activity. Therefore, a supported catalyst with high activity for producing syndiotactic styrenic polymer is highly expected. The present inventors have developed a supported catalyst with high activity, which is used to prepare a syndiotactic styrenic polymer with high productivity and with significantly diminished reactor fouling when a stirring-tank reactor is employed.
A feature of the present invention is the provision of a supported catalyst with high activity for preparing syndiotactic styrenic polymer.
Another feature of the present invention is the provision of a supported catalyst with high activity for preparing syndiotactic styrenic polymer with high productivity.
A further feature of the present invention is the provision of a supported catalyst with high activity for preparing syndiotactic styrenic polymer, which can significantly diminish reactor fouling when a stirring-tank reactor is employed.
A further feature of the present invention is the provision of syndiotactic styrenic polymer powder with good flowability and morphology.
The above and other objects and advantages of this invention will be apparent from the ensuing disclosure and appended claims.
The supported catalyst according to the present invention comprises (A) a support of organic or inorganic powder with a high-surface area, (B) a polymer coated onto the support and (C) a homogeneous transition metal compound as essential component, the polymer (B) functioning an insulation layer between the support and the metal compound. The supported catalyst can contain optionally (D) alkyl aluminoxane and/or (E) alkyl aluminum compound. By using the supported catalyst provided by the present invention, the productivity of styrenic polymer is much increased and the reactor fouling was significantly reduced. The supported catalyst can be used in combination with a cocatalyst, preferably an alkyl aluminoxane. The styrenic polymer powder such produced by the present invention has good flow-ability and good morphology demonstrating a great deal of industrial applicability.